Tappet for a valve drive of an internal combustion engine

ABSTRACT

A tappet (1) for a valve drive or an internal combustion engine comprising a hollow cylindrical housing (2) guided for axial displacement by a jacket (3) thereof in a reception bore (4) of a cylinder head (5), an end of the housing (2) facing a cam (8) being closed by a bottom (7), a guide sleeve (11) arranged concentrically in the tappet (1) for guiding a hydraulic clearance compensation element (10) being supported by a connected web (12) against the jacket (3) which is made of two separate, bush-like sections (14,15) of approximately equal diameter separated from each other in the region of a central transverse plane, and a first cup-shaped section (14) of the jacket (3) being connected at a cam-proximate end thereof to the bottom (7), characterized in that the second, lower section (15) comprises an extension (16) starting axially adjacent the first section (14) and extending into an immediate vicinity of the bottom (7), the second section (15) with its extension (16) has a smaller wall thickness than the first section (14) and is made as a sheet metal or plastic element, the extension (16) bears by an outer peripheral surface (17) thereof against an inner peripheral surface (18) of the first section (14).

The invention concerns a tappet for a valve drive of an internalcombustion engine comprising a hollow cylindrical housing guided foraxial displacement by a jacket thereof in a reception bore of a cylinderhead, an end of the housing facing a cam being closed by a bottom, aguide sleeve arranged concentrically in the tappet for guiding ahydraulic clearance compensation element being supported by a connectedweb against the jacket which is made of two separate, bush-like sectionsof approximately equal diameter separated from each other preferably inthe region of a central transverse plane, and a first cup-shaped sectionof the jacket being connected at a cam-proximate end thereof to thebottom.

A tappet of this type is described in EP-A-04 85 007 and likewisecomprises a tappet jacket divided along a central transverse plane andhaving an upper section closed by a bottom. A web comprising a guideportion for receiving a hydraulic clearance compensation element extendsradially inwards from the lower section. An oil channel leads through aplastic cushion arranged in the annular oil reservoir into the centraloil reservoir for supplying hydraulic medium to the clearancecompensation element. A drawback of the tappet known from EP-A-04 85007, which is considered as the generic prior art, is that the bottomtogether with the two separate jacket sections and the web is arelatively solid structure. Moreover, the plastic cushion arranged inthe annular oil reservoir also has a detrimental effect on the totalmass and thus also on the oscillating mass of the valve drive. Due tothe fact of direct suction into the reservoir which is situated at ahigher lever, there exists the inherent danger of air and oil foam beingsucked into the high pressure chamber during the base circle phase ofthe tappet. This is particularly unfavorable when the internalcombustion engine is operated only for short periods, for example in theso-called "taxi" or "stop-and-go" mode and results in an undesiredyielding of the valve drive during the high-pressure phase of thetappet, i.e. during valve lift. In addition, the oil transfer beadarranged in the bottom detracts from the rigidity of the bottom which asa result has to be made with a larger thickness.

A further prior art document, EP-A-04 43 146, discloses a tappet whosejacket is made integrally with the bottom and the jacket itself is alsoa one-piece structure. Within the tappet, there is arranged coaxial withthe jacket surface, a thin-walled guide element comprising an ascendinggroove for hydraulic oil. This prior art document too, does not discloseany means for reducing the mass of the tappet because its jacket has arelatively solid configuration and is made integrally with the bottom.Moreover, the aforesaid guide element also increases the total mass.

It is therefore an object of the invention to provide a tappet of theprecited type in which the discussed drawbacks are eliminated and which,particularly, is simple to manufacture and possesses a high strength.

The invention achieves this object by the fact that the second, lowersection comprises an extension starting axially adjacent the firstsection and extending into the immediate vicinity of the bottom, thesecond section with its extension has a smaller wall thickness than thefirst section and is made as a sheet metal or plastic element, theextension bears by an outer peripheral surface thereof against an innerperipheral surface of the first section, the web extends from abottom-proximate edge of the extension in cam-remote direction tosupport the guide sleeve, an annular groove is formed in the secondsection between a cam-remote edge of the first section and a facing edgeof the second section oriented towards the cam, and at least one channelextends from the annular groove to feed oil into the tappet interior,said channel extending axially between the outer peripheral surface ofthe extension and the inner peripheral surface of the first section.

The two-piece configuration of the tappet described herein constitutes amajor step in obtaining a light-weight structure. The lower section ofthe jacket not only fulfils a guiding function but also the function ofoil path reversal of the hitherto separately made guide sleeve. Thelower section is thinner and therefore also simpler to manufacture sothat assembly and manufacturing costs are reduced as compared toconventional tappets. The light-weight tappet of the invention permits areduction of the valve spring forces as well as a reduction of thethickness of the bottom with its cam-contacting surface. The optimumdimensions of the light-weight valve drive are determined empiricallyand lead to a minimization of the driving energy required for operatingthe valve drive. The aforesaid annular groove in the lower section makesit possible to avoid additional machining and do without furthercomponents for assuring a reliable oil supply to the clearancecompensation element.

The one-piece configuration of the web with the guide sleeve and theextension results in an embodiment which is particularly favorable fromthe manufacturing point of view. Preferably, all the elements of thisone-piece component are thin-walled and made by chipless shaping, andthe tappet may also be used as a light-weight mechanical tappet in whichcase, however, the guide sleeve and the web can be dispensed with. Theinvention covers not only the funnel-shaped arrangement described hereinbut also other configurations such as, for example, a radially extendingweb with orthogonal extensions.

Another feature of the invention concerns a simple measure for removingair possibly contained in an oil reservoir of the tappet. Between theextension of the second section and the inner peripheral surface of thefirst section, there is formed at least one further, axially extendingchannel into which at least one deaeration bore through the firstsection opens, the channel being configured separately from the annulargroove.

In a further embodiment of the invention, the first and the secondsections are connected to each other by a joining of their constitutivematerials by welded, soldered or glued joints which can beadvantageously arranged at different locations. It is also conceivableto use shape-locked or force-locked connections such as snap or clampjoints, interlocking and the like.

Other measures concern additional measures for weight optimization andwear reduction in the present tappet. For example, it would beconceivable to make the upper section out of an engineering ceramic orto use aluminium as the base material for at least one of the twosections and to reinforce only highly loaded parts.

The disc-shaped wear-resistant element can be configured, for example,as a hardened steel plate but may optionally also be made of a ceramicmaterial.

Particularly with a view to a contact of the outer wall of the tappetwith an aluminium bore of a cylinder head, the cup-shaped section may bemade of brass or coated with brass because this has a very conduciveeffect on the wear behavior of such a contact.

The aforesaid disc-shaped wear-resistant element can be arranged, forexample, in a separate lodging in the bottom but may also be made tocover the entire width of the bottom.

The feature wherein both sections (14 and 15) are made of a steel whichis weldable in a hardened state excludes distortion which can occur dueto the heat treatment which normally follows welding.

Finally, to obtain a further reduction of weight, the lower section orthe extension may comprise window-like apertures.

The invention is not limited to the features described in the claims.Conceivable is also a combination of individual features of the claimswith one another and with the disclosures contained in the discussion ofadvantages and the examples of embodiment.

The invention is represented in the drawings in which:

FIG. 1 shows a transverse cross-section through a tappet of theinvention, and

FIG. 2 shows a modified cross-section according to FIG. 1.

FIG. 1 shows a tappet 1 of the invention which comprises a hollowcylindrical housing 2 guided by its jacket 3 for axial displacement in areception bore 4 of a cylinder head 5. One end of the tappet 1 is closedby a circular bottom 7 whose end face 9 directed towards a cam 8 iscontacted by said cam. A hydraulic clearance compensation element 10 isarranged coaxial with the jacket 3 within a guide sleeve 11 in thetappet interior. The guide sleeve 11 is made integrally with afunnel-shaped web 12 which, in a cam-remote direction, defines aconcentric oil reservoir 13 from which hydraulic medium is supplied tothe clearance compensation element 10. The jacket 3 of the housing 2 isdivided along a central transverse plane into two parts and thuscomprises a first and a second section 14, 15. At its end facing thecam, the first section 14 is closed by the bottom 7. The second section15 is arranged axially adjacent to the first section 14 in cam-remotedirection and comprises a hollow cylindrical extension 16 extending incam direction. An outer peripheral surface 17 of the extension 16 bearsat least portion wise against an inner peripheral surface 18 of thefirst section 14. Starting from an upper edge 19 of the extension 16,the web 12 is formed integrally therewith and merges into the guidesleeve 11. An annular groove 22 for oil supply to the clearancecompensation element 10 is formed between mutually facing edges, 20 and21, of the first and second sections 14 and 15 respectively. Between theextension 16 and the first section 14, there extends an axially parallelchannel 23 leading from the annular groove 22 to the oil reservoir 13.

As can be seen in the right half of the figure, a further channel 24 canbe defined by the extension 16. One end of this channel 24 communicateswith the oil reservoir 13 while its other end opens into a deaerationbore 25 made in the first section 14. In the cam-remote direction, thischannel 24 is separated from the annular groove 22.

Different methods of joining the two sections 14, 15 of the housing 2are shown in FIG. 2. For this purpose, a welded joint 26, but also asoldered or glued joint 27 between the extension 16 and the firstsection 14, may be used.

The bottom 7 can be made of a polymeric material or reinforced withembedded fibers or particles 28. For the purpose of wear protection, itis also possible to apply a wear-resistant coating layer 29, forexample, of a ceramic or other suitable material.

I claim:
 1. A tappet (1) for a valve drive of an internal combustionengine comprising a hollow cylindrical housing (2) guided for axialdisplacement by a jacket (3) thereof in a reception bore (4) of acylinder head (5), an end of the housing (2) facing a cam (8) beingclosed by a bottom (7), a guide sleeve (11) arranged concentrically inthe tappet (1) for guiding a hydraulic clearance compensation element(10) being supported by a connected web (12) against the jacket (3)which is made of two separate, bush-like sections (14, 15) ofapproximately equal diameter separated from each other in the region ofa central transverse plane, and a first cup-shaped section (14) of thejacket (3) being connected at a cam-proximate end thereof to the bottom(7), characterized in thatthe second, lower section (15) comprises anextension (16) starting axially adjacent the first section (14) andextending into an immediate vicinity of the bottom (7), the secondsection (15) with its extension (16) has a smaller wall thickness thanthe first section (14) and is made as a member of the group consistingof a sheet metal and plastic element, the extension (16) bears by anouter peripheral surface (17) thereof against an inner peripheralsurface (18) of the first section (14), the web (12) extends from abottom-proximate edge (19) of the extension (16) in a cam-remotedirection to support the guide sleeve (11), an annular groove (22) isformed in the second section (15) between a cam-remote edge (20) of thefirst section (14) and a facing edge (21) of the second section (15)oriented towards the cam, and at least one channel (23) extends from theannular groove (22) to feed oil into the tappet interior, said channel(23) extending axially between the outer peripheral surface (17) of theextension (16) and the inner peripheral surface (18) of the firstsection (14).
 2. A tappet of claim 1 wherein the web (12) is made in onepiece with the guide sleeve (11) and the extension (16) and extendssubstantially funnel-shaped in said cam-remote direction.
 3. A tappet ofclaim 1 wherein at least one further, axially extending channel (24) isarranged between the extension (16) of the second section (15) and theinner peripheral surface (18) of the first section (14), at least onedeaeration bore (25) passing through the first section (14) opens intosaid further channel (24), and said further channel (24) is separatedfrom the annular groove (22).
 4. A tappet of claim 1 wherein the firstsection (14) is connected to the second section (15) by a joining ofmaterials.
 5. A tappet of claim 4 wherein the joining of materials isobtained by a welded, soldered or glued joint (26, 27).
 6. A tappet ofclaim 4 wherein the joint is arranged along an annular groove (22) whichextends between said cam-remote edge (20) of the first section (14) andsaid facing edge (21) of the second section (15) oriented towards thecam.
 7. A tappet of claim 4 wherein the joint is arranged in an annularregion between the outer peripheral surface (17) of the extension (16)and the inner peripheral surface (18) of the first section (14).
 8. Atappet of claim 1 wherein at least one member of the group consisting ofat least one of the two sections (14, 15) and the bottom (7) is made ofa light-weight material.
 9. A tappet of claim 1 wherein the cup-shapedsection (14) of the housing (2) is made of aluminium.
 10. A tappet ofclaim 1 wherein at least one member of the group consisting of the lowersection (15) and the extension (16) comprises window-like apertures(30).
 11. A tappet of claim 1 wherein at least one of the two sections(14, 15) is made of a ceramic material.
 12. A tappet of claim 1 whereinboth sections (14 and 15) are made of a steel which is weldable in ahardened state.
 13. A tappet of claim 1 wherein at least one member ofthe group consisting of at least one of the two sections (14, 15) andthe bottom (7) is made of a polymeric material and is reinforced withfibers, particles or lattices (28) embedded therein.
 14. A tappet ofclaim 1 wherein at least one member of the group consisting of thejacket (3) of the housing (2) and a cam-proximate end face (9) of thebottom (7) comprises a wear-resistant coating layer (29).
 15. A tappetof claim 8 wherein at least one of the two sections (14, 15) is made ofa ceramic material.
 16. A tappet of claim 6 wherein the joint isarranged along an annular groove (22) which extends between saidcam-remote edge (20) of the first section (14) and said facing edge (21)of the second section (15) oriented towards the cam.
 17. A tappet ofclaim 6 wherein the joint is arranged in an annular region between theouter peripheral surface (17) of the extension (16) and the innerperipheral surface (18) of the first section (14).